War effect Researchers in the Netherlands have been able to shed more light on how combat experiences change the brains of soldiers.

Two years ago, a study showed that soldiers returning from Afghanistan had heightened activity in the part of the brain that processes fear - the amygdala.

But in a new study, published today in the journal Molecular Psychiatry, the researchers found this activity returned to normal after 18 months.

But they say that doesn't mean the soldiers' brains as a whole returned to normal.

The study measured the response of 23 soldiers who had returned from a four-month deployment in Afghanistan and compared them with 16 non-deployed soldiers. Each was instructed to complete a 'face matching task' while their brain activity was measured in an fMRI scanner.

Assistant Professor Guido van Wingen, a neuroscientist at Radboud University , says soldiers who had recently returned from deployment had heightened activity in the amygdala when shown an angry and fearful face.

"[This] suggests that it's due to the stressful situation they're in for months in a row where they continuously have to be vigilant for potential danger in the environment," says van Wingen.

But when the researchers conducted the same tests on the soldiers 18 months later, the effect had disappeared.

"What we now observed is that amygdala reactivity does decrease again to what it was, a similar pattern as before deployment," he says.

"But what we also observed is that the structure implicated in controlling amygdala functioning, in the pre-frontal cortex, which is more kind of the control centre in the brain, was still changed."

Long-term effects unknown

Van Wingen says that while direct reactions and responses to the environment might normalise, more research is needed to understand the subtle changes in the pre-frontal cortex.

"Those changes might also affect the next potential stressful episode."

David Jamison, national president of the Australian Defence Force Welfare Association, says it's a relief to hear that soldiers' amygdalas can return to normal.

But he says the experience of the soldiers in the study doesn't reflect that of Australian soldiers who may undergo multiple deployments.

"You're lucky to get an 18 month interval between deployments," says Jamison. "We're a bit worried about the cumulative effect."

He adds that even if the brain structure isn't permanently changed that doesn't mean soldiers won't suffer mental illness like post-traumatic stress disorder which can take longer than 18 months to manifest.